"It's awfully important to know the category before you lay your money down," he said. Discovering a child's real talents would be even better, he added. "Your mission as a parent is to say not 'How smart is my kid?' but 'How is my kid smart?' " he said. "You focus in on that and then, wherever the kid goes to college, he'll know, 'This is what I'm good at.' "

Q : The function of "smart" in "How smart is my kid?" is an adjective and "smart" in "How is my kid smart" is a noun , isn't it?

Incidentally, 'How is my kid smart?' is a slightly unusual construction, for more standard 'IN WHAT WAY(S) is my kid smart?'. It is deliberately expressed using 'how' in order to effect a connection with the previous question.